The subject matter of this invention relates to the field of energy storage and utilization and in particular to an improved battery and to a rechargeable electrode for use therein. More particularly, the invention relates to a battery having an anode formed from a primarily non-equilibrium disordered material designed to have a large number of catalytically active sites and also a large number of storage sites to store a substantial amount of hydrogen with the chemical bonding designed to efficiently store and release the hydrogen. The battery anode is charged to store hydrogen and discharged to release the stored hydrogen to produce an electrical current.
The present invention frees the anode material design from the limits of crystalline stoichiometry and compositions and allows a whole range of reversible hydrogen storage bonding in the material. The superior battery of the invention has attained a high density energy storage, efficient reversibility, high electrical efficiency, bulk hydrogen storage without substantial structural change or poisoning and hence long cycle life and deep discharge capability. The disordered material preferably is formed from lightweight materials to give a high storage capacity and is made from low cost materials. Thus, for the first time a quantum step forward in battery performance has been attained.
The storage of energy has been one of the great scientific, technological and economic problems in the energy field and most particularly the storage of electrical energy.
The demand for the storage of electricity is increasing at a rapid rate as the world becomes increasingly more dependent on electricity generated from both large base load plants and from renewable, but variable energy sources. It has been estimated that the total energy storage required in the United States by the year 2000 will be about 200 trillion Wh (watt-hours). Batteries have particular advantages for storage applications since:
(1) they store and release electric energy,
(2) they are portable and modular and hence have very flexible uses,
(3) they are relatively easy to manufacture,
(4) they are relatively compact,
(5) they are compatible with and have the ability to follow efficiently the instantaneous variations in the demand for electricity, while at the same time providing regulation of the output, and
(6) they provide local storage and hence reduce transmission and distribution costs.
While each of the above advantages of batteries potentially are available, there remain many problems with conventional batteries. For example, conventional batteries containing lead, mercury or cadmium are environmental contaminants, and therefore cannot easily be disposed of. Conventional batteries have serious materials problems which effect shelf life and cycle life and make them uneconomical for many applications.
The battery field has long been recognized as being a field of slow development rather than the quantum leap forward necessary to permit cost effective use of batteries on a truly large scale basis. It has been stated that "Battery technology is a classic example of an evolving process. We take one step back for every two forward. Most systems that are receiving attention today have been around for decades, and you really can't point to any breakthroughs." A battery, both primary and secondary, with high energy and power density, low cost and long life with many rechargeable cycles is necessary to answer the needs for energy storage and portability which are basic requirements for energy storage. Because of the failure to achieve breakthroughs to solve critical problems in existing battery technology, batteries have achieved only a small fraction of their true potential use.
The applications and potential applications for batteries are too numerous and familiar to enumerate, but some applications are of particular interest for secondary batteries. A secondary battery is a battery which is capable of being recharged after use so that it can be used again to supply electrical energy. Secondary batteries have particular utility in portable applications, such as portable electronic devices, and are particularly suitable for the utilization of solar energy and other electricity generators, such as thermoelectric generators, especially for remote use. It is estimated that the size of the battery market for solar energy applications and the market for electric vehicle batteries will be in the hundreds of gigawatt hours by the year 2000. While great progress has been made in the photovoltaic conversion of solar energy into electricity, there has been little progress in the companion or supporting technology for storage of electrical energy. The development of a truly cost effective technology for storing electrical energy in a convenient reversible form would expand enormously the potential for the utilization of photovoltaic power generation.
The use of electric vehicles to replace fossil fuels is very important. It has been estimated that more than twothirds of all our energy, for example, from automobile exhausts or power plants, is wasted and given off to the environment. The Canadian House of Commons' Special Committee on Alternative Energy and Oil Substitution has stated: "The main problem with developing a practical and competitive electrical vehicle has been the inability to produce inexpensive, reliable, lightweight, energy-dense and durable batteries. A large variety of battery systems is presently being tested but none has emerged which completely overcomes all of these difficulties. Analysts continue to say a quantum leap in battery technology must be made before electrical vehicles become competitive with conventional cars in the automobile market."
The Department of Energy (DOE) has developed target goals for electric vehicles. The 1982 goal is to obtain a battery capacity of 56 Wh/kg which would power an electric vehicle for 100 miles. The best commercially attainable capacities are for lead acid and nickel cadmium batteries which are reported as 37 Wh/kg and 39 Wh/kg, which are well below the 1982 DOE goal. These two types of batteries account for about ninety percent of the secondary battery market. While it has been estimated that a 100 mile range would take care of about ninety percent of the driving needs of the urban population, a recent survey made for DOE shows that consumers are not likely to purchase electric vehicles in large quantities until their range is extended to 200 miles. This figure is beyond the range of existing batteries, but is within the capability of the battery of the present invention. For example, the battery of the present invention can be greatly reduced in size and weight while still producing the desired power, because of the high energy storage density. This greatly increased density gives rise to new battery applications which previously were prohibited, because sufficient power was not available for a given battery size and weight.
The components of a conventional secondary battery such as a nickel-cadmium cell are the anode formed from a cadmium material, and the cathode formed from a nickel hydroxide material. The anode and cathode typically are spaced apart in the cell containing an alkaline electrolyte, such as KOH. The battery is charged upon application of an electric current to the anode as shown in the following equation: EQU Cd(OH).sub.2 +2e.sup.- .fwdarw.Cd+2OH.sup.-
When the battery is utilized (discharged) the reverse reaction occurs to provide a supply of electrons: EQU Cd+2OH.sup.- .fwdarw.Cd(OH).sub.2 +2e.sup.-
Over the years, many different electrochemical systems have been developed for battery applications. Such systems, such as zinc-chloride, nickel-zinc, lithium-metal sulfide and nickel-hydrogen have been explored, but have only found limited and specialized applications. The nickel-zinc system has a low cycle life and is expensive. The zinc-chloride battery operates with hazardous chemicals and has a very complex recharging system along with being expensive. Most lithium-metal sulfide systems operate at only very high temperatures of above 350.degree. C. The nickel-hydrogen system is a high pressure, large and expensive system utilized for some specialized space applications.
Each of the available systems provides one or more significant impediments to widespread use, such as low energy density, high operating temperatures, hazardous and/or toxic chemicals, expensive materials or operating procedures. Lead and cadmium systems, for example, both present disposal problems and neither system meets even the 1982 DOE goals. Further, battery electrodes are notorious for their susceptibility to corrosion which limits life time and cycling life for secondary batteries. The large-scale utilization of batteries for storage of electricity has remained blocked because of the fundamental limitations in the technology.
Some research has been conducted involving hydrogen rechargeable secondary batteries. However, a basic understanding resulting in a viable approach to optimizing such batteries has not been forthcoming in the scientific or patent literature. One example of such efforts is U.S. Pat. No. 3,874,928. These research efforts have not resulted in any commercial utilization of this battery technology. As a matter of fact, the prior research results have suggested no significant improvement over the conventional nickel cadmium system and hence have resulted in the hydrogen storage battery techniques apparently being ignored or abandoned.
Secondary batteries using a hydrogen rechargeable electrode operate in a different manner than the lead acid and other prior systems. The battery utilizes an anode which is capable of reversibly electrochemically storing hydrogen and employs a cathode of nickel hydroxide material which is used in a conventional secondary battery. The anode and cathode are spaced apart in an alkaline electrolyte. Upon application of an electrical current to the anode, the anode material M is charged by the absorption of hydrogen: EQU M+H.sub.2 O+e.sup.- .fwdarw.M--H+OH.sup.-
Upon discharge the stored hydrogen is released to provide an electric current: EQU M--H+OH.sup.- .fwdarw.M+H.sub.2 O+e.sup.-
The reactions are reversible and this is also true of the reactions which take place at the cathode. As an example, the reactions at a conventional nickel hydroxide cathode as utilized in a hydrogen rechargeable secondary battery are as follows:
Charging: Ni(OH).sub.2 +OH.sup.- .fwdarw.NiOOH+H.sub.2 O+e.sup.- PA1 Discharging: NiOOH+H.sub.2 O+e.sup.- .fwdarw.Ni(OH).sub.2 +OH.sup.-
The battery utilizing an electrochemically hydrogen rechargeable anode offers important potential advantages over conventional secondary batteries. Hydrogen rechargeable anodes should offer significantly higher specific charge capacities than lead anodes or cadmium anodes, however, prior anodes have not levied up to that potential because of the limitations of the materials utilized. Thus more electrical energy per unit weight should be possible with such batteries making them particularly suitable for battery powered vehicles and other mobile applications. Furthermore, lead acid batteries and nickel-cadmium type secondary batteries are relatively inefficient, because of their low storage capacity and cycle life.
The materials used for the hydrogen rechargeable anode of the battery are of utmost importance since the anode must efficiently perform a number of functions within useful operating parameters in order to have an efficient charge/discharge cycle. The material must be capable of efficiently storing hydrogen during charging with insignificant self discharge until a discharge operation is initiated. Since complete reversibility of the charge/discharge reactions is necessary a highly stable bonding of hydrogen to the storage sites of the anode is not desired. On the other hand, it is also undesirable if the bonds between the hydrogen atoms and the anode material are too unstable. If the bonds are too unstable during charging the dissociated hydrogen atoms may not be stored by the anode, but may recombine to form hydrogen gas such as in the electrolysis of water. This can result in, low efficiencies, loss of electrolyte and inefficient charging.
The materials for storing hydrogen which have been proposed in the prior art for use as a hydrogen chargeable anode for secondary batteries have generally been limited to materials which are primarily crystalline structures. In crystalline materials the catalytically active sites result from accidently occurring, surface irregularities which interrupt the periodicity of the crystalline lattice. A few examples of such surface irregularities are dislocation sites, crystal steps, surface impurities and foreign absorbates.
A major shortcoming with basing such anode materials on crystalline structures is that irregularities which result in active sites typically only occur in relatively few numbers on the surface of a crystalline material. This results in a density of storage sites which is relatively low. Of equal importance is that the type of sites available are of an accidental nature and are not designed into the material as are those of the present invention. Thus, the efficiency of the material for the storage of hydrogen and the subsequent release to form water is substantially less than that which would be possible if a greater number and variety of sites were available.
All of the previous attempts to utilize hydrogen in secondary batteries have proven to be unsuccessful, because the crystalline materials have one or more limiting factors which prevent commercialization. The invention herein provides a new and improved battery having an electrode formed from disordered non-equilibrium material which does not suffer from the disadvantages and limitations of the prior art batteries containing crystalline electrode materials.